Wood fibre based panels with a thin surface layer

ABSTRACT

Building panels with a thin and embossed surface layer and a sub layer between a surface layer and a core.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Ser. No. 61/042,938,filed on 7 Apr. 2008, and U.S. Ser. No. 12/270,257, filed on 13 Nov.2008, both of which are incorporated herein in their entirety.

TECHNICAL FIELD

The invention generally relates but is not limited to the field of woodfibre based building panels with a thin surface layer, preferably floorpanels. The invention relates but is not limited to building panels withsuch surface layer and to equipment and methods to produce such panels.

FIELD OF APPLICATION OF THE INVENTION

The present invention is particularly suitable for use in floatingfloors, which are formed of floor panels with a wood fibre core and athin decorative wear resistant surface. The following description ofprior-art technique, problems of known systems and objects and featuresof the invention will therefore, as a non-restrictive example, be aimedabove all at this field of application and in particular at flooringswhich are similar to traditional wood fibre based laminate floorings.

It should be emphasized that the invention can also be used in otherapplications as for example wall panels, ceilings, and furniturecomponents and similar.

BACKGROUND

Wood fibre based direct pressed laminated flooring usually comprises acore of a 6-12 mm fibre board, a 0.2 mm thick upper decorative surfacelayer of laminate and a 0.1-0.2 mm thick lower balancing layer oflaminate, plastic, paper or like material.

A laminate surface generally comprise two paper sheets, a 0.1 mm thickprinted decorative paper and a transparent 0.05-0.1 mm thick overlayintended to protect the decorative paper from abrasion. The transparentoverlay, which is made of α-cellulose fibres, comprises small hard andtransparent aluminum oxide particles, which gives the thin surface layera high wear resistance.

The printed decorative paper and the overlay are impregnated withmelamine resin and laminated to a wood fibre based core under heat andpressure. The two papers have prior to pressing a total thickness ofabout 0.3 mm and they are after pressing compressed to about 0.2 mm.

Other common thin surface materials are wood veneer and foils, which areglued to a core.

The most common core material is fibreboard with high density and goodstability usually called HDF—High Density Fibreboard with a densityexceeding 800 kg/cm². Sometimes also MDF—Medium Density Fibreboard—witha density of 600-800 kg/cm² is used as core. Other core materials couldalso be used such as particleboard, plywood, and plastic materials andsimilar.

A balancing layer is generally applied on the rear side of the board inorder to keep the panel flat when humidity changes.

HDF is produced as follows: Roundwood such as for example pine, larch orspruce are reduced to wood chips and then broken down into individualfibres in a refiner. The fibres are thereafter mixed with binders andthen subjected to high pressure and temperature to form a board.

Floor panels with such thin surface layer are very cost effectivecompared to for example solid wood, stones and tiles. The majordisadvantage is that properties related to deep surface structures,impact resistance and sound are inferior to the real products that theyaim to copy.

Laminate floorings could be produced with very advanced designs where aprinted pattern is coordinated with an embossed structure of thesurface. The embossing is made during lamination when the surface ispressed against a steel sheet with an embossed structure.

The depth of the embossing is limited by the paper that could be damagedwhen the embossing is made with sharp edges or to a depth, which exceedsa few tenths of a millimetre. The embossing is mainly obtained by acompression of the overlay and the decorative paper. Embossed surfacessimilar to a rough stone surface or a hand scraped wood surface or deepgrooves that could be used to make bevels in a panel are not possible tomake with the present pressing technology and with a reasonable coststructure maintaining the present technical properties and design.

Several methods have been used to increase the depths of the embossedsurface structure.

It is known that one or several impregnated core paper sheets could beapplied under the decorative surface paper and that deeper embossing upto 0.3-0.4 mm could be reached by a compression of the surface layer andthe core paper. A similar method is described in WO 2004/067874. Suchmethods are expensive due to the fact that the pressure and pressingtime must be increased from the normal level of 300-400 N/cm² to about800 N/cm² and additional expensive material such as a core paper must beincluded in the panel under the decorative paper. Usually even thebalancing layer has to be made thicker and this will increase the costfurther.

It is also known that bevels and surface embossing could be made by acompression of the surface papers and the upper part of the core underthe surface layer. Such a method is described in WO 03/078761 (ValingeInnovation AB) or WO 2006/066776. This method has several disadvantages.It could only be used in panels with a soft core such as MDF. This givesa low impact resistance and it is difficult to form high quality lockingsystems in such soft materials. In panels with a HDF core only limitedand local embossing could be reached with conventional presses used inlaminate production where the surface layer is formed and attached to acore (DPL technology). A considerable higher pressing force and longerpressing time is generally required to form surfaces similar to stoneand rough wood surfaces.

Sufficient impact resistance can only be reached if thin surface layersare applied on a rather thick core with a high density. This means thatthe core material will be expensive and generally a board quality mustbe used that has better properties than what is needed for the overallstability of the panel and the strength of the locking system.

Definition of Some Terms

In the following text, the visible surface of the installed floor panelis called “front side”, while the opposite side of the floor panel,facing the sub floor, is called “rear side”. The sheet-shaped materialthat comprises the major part of a floor panel is called “core”. Whenthe core has a surface layer closest to the front side and preferablyalso a balancing layer closest to the rear side, it forms asemi-manufacture, which is called “floor board” or “floor element” inthe case where the semi-manufacture, in a subsequent operation, isdivided into a plurality of floor elements. When the floor elements aremachined along their edges so as to obtain their final shape with thejoint system, they are called “floor panels”. By “surface layer” ismeant all layers applied to the core closest to the front side andcovering preferably the entire front side of the floorboard. By“decorative surface layer” is meant a layer, which is mainly intended togive the floor its decorative appearance. “Wear layer” relates to alayer, which is mainly adapted to improve the durability of the frontside.

By “horizontal plane” is meant a plane, which extends parallel to theouter part of the surface layer. By “horizontally” is meant parallel tothe horizontal plane. By “up” is meant towards the front face and by“down” towards the rear face.

SUMMARY OF THE INVENTION

Wood fibre based floorings with thin surface layers similar to laminateand wood veneer floorings could capture a considerably larger marketshare if deep embossing and increased impact resistance could be reachedin combination with a cost effective production method.

An overall objective of an embodiment of the present invention is toprovide a building panel, preferably a floor panel, with a thin surfacelayer, which has a more attractive surface design and/or better surfaceproperties and/or cost structure than present known floorings withconventional thin surface layers.

A specific objective of an embodiment of the invention is to provide amethod to produce a floor panel with new attractive design features suchas deep embossing which preferably could be combined with high impactand wear resistance, improved sound properties and cost effectiveproduction.

The problem has been solved, contrary to the known methods where severalpaper layers or a core is compressed, with a method and a panel, whichcomprises a sub layer between a surface layer and a core. This sub layercomprises or consists of small individual fibres and an uncured binderand is applied on the core as a powder. The small fibres are not bondedto each other as for example fibres in paper layers and a HDF core, andcould easily be compressed, formed and displaced in all directionsduring a part of a pressing operation until the binder cures. Theuncured sub layer behaves similar to a paste or a liquid substance andcreates a uniform counter pressure in all parts under the surface layereven in surface parts with deep and sharp embossing. The result is animproved and easier forming with lower pressing force and improvedsurface quality. A thin surface layer will usually not be damaged,significantly or at all, during pressing and the sub layer will aftercuring provide a strong base for the thin surface layer. Such a basecould be stronger than the core and improved impact resistance could bereached.

According to a first aspect of an embodiment of the invention aproduction method is provided to produce a floor board comprising a woodfibre based core, a thin surface layer and a sub layer between thesurface layer and the core. The sub layer comprises or consists of woodfibres and a binder. The method comprises the steps of:

-   -   mixing particles comprising wood fibres and an uncured binder        for the sub layer,    -   applying the wood fibres and the uncured binder for the sub        layer on the core,    -   applying a surface layer on the wood fibres and the uncured        binder,    -   bringing the core (6), the surface layer (5), the wood fibres        (14) and the uncured binder (19) under increased pressure and        temperature and forming them to a floor board (1) by curing the        binder (19).

The first aspect offers the advantage that the sub layer could beproduced with higher density than the core and this could give the floorpanel a high impact resistance even in the case when the surface layeris thin or the core rather thin or soft. A core material could also havea rather uneven core surface, which could be filled by the sub layer.This makes it possible to use for example particleboard or un-sanded HDFboard in a DPL production based on one decorative paper and one overlay.

The wood fibre based sub layer is very cost efficient compared to forexample a core paper. The curing time and the required pressure force inthe press could be the same as for conventional laminate floorings.

The sub layer could comprise colour pigments with a different colourthan the surface layer and decorative grooves, where the surface layeris removed and the sub layer is visible, could be formed.

The sub layer could also comprise particles, for example cork particles,which could give the floor panel improved sound properties andflexibility.

A cork layer could be used in combination with known surface materialssuch as laminate, resilient surfaces, fibre based surfaces, wood, woodveneer, linoleum, cork veneer and similar. Several advantages could bereached. A thin surface layer, for example a wood veneer could beapplied, prior to pressing, on a sub layer comprising cork particles andbinders. Pressing could take place against a press plate, which couldcreate a deep embossing, or deep grooves. The thin surface layer will beformed and laminated to the sub layer. The thin surface layer will notbe damaged since the cork particles will be compressed and formedaccording to the structure of the press plate. This forming technologycould also be used in a panel where the sub layer comprises wood fibresor other type of fibres that could be formed by pressing.

According to a preferred embodiment of the first aspect, the methodfurther comprises the step of pressing the surface layer with anembossed pressing matrix such that the surface layer obtains upperportions and embossed portions which are lower than the upper portions,by shaping of the sublayer. The embossed portions are preferablyobtained by compression of the sublayer located under the embossedportion and/or by shifting fibres located under the embossed portion tothe upper portions.

In a preferred embodiment a part of the sub layer is more compressedunder an embossed portion than a part of the surface layer located underan upper portion. A part of the sub layer that is more compressed withhave a greater density than a part of the surface layer in a lesscompressed part.

An embodiment of the invention offers the advantages that the sub layerduring the initial stage of the pressing is uncured and soft andcomprises particles, which easily could be displaced during pressing.Very deep embossing could be formed with normal pressing force. Deepsurface embossing of for example up to 0.5 mm and even more could easilybe reached with a surface layer comprising a decorative paper, a foil,wood veneer and similar. The embossing is preferably formed when thesurface is pressed against an embossed steel sheet or belt or a papermatrix.

A major advantage is that deep embossing of the surface layer and thesub layer could be formed without any compression of the core material.A compression of the core material is however not excluded. Such acompression of the core could take place if the sub layer for example isvery thin.

The sub layer could comprise fibres and binders, which are suitable fora second pressing step where further embossing and forming could beformed in a press or with roll forming.

The thin surface layers should preferably have a thickness beforepressing of about 0.3-1.0 mm. Thinner layers with a thickness of 0.1-0.2mm are not excluded and very deep embossing could be formed with suchthin surface layers of for example foils and papers. The surface layercould also be a print, paint or coating that is applied prior or afterthe pressing. Thicker layers of more than 1 mm could also be used, forexample linoleum, resilient floor surfaces and similar.

The production could be made in continuous or discontinuous presses.

According to another preferred embodiment of the first aspect a surfacelayer is provided which comprises a homogenous mix of wood fibres, wearresistant particles binders and colour pigments. Such surface layer isbelow referred to as Solid Laminate Surface Layer. The surface layerpreferably comprises natural resins, e.g. lignin, of bio based material,e.g. from wood.

The surface layer and the sub layer are in this embodiment rathersimilar regarding material properties and material composition. Thesurface layer comprises however wear resistant particles for examplealuminum oxide and colour pigments. The binders and the fibres could besimilar in both layers. The size of the fibres and the resin contentcould however vary. Very deep surface embossing and bevels of more than1 mm depth could easily be formed.

According to a second aspect of an embodiment of the invention abuilding panel is provided comprising a thin surface layer, a wood fibrebased core and a sub layer between the surface layer and the core. Thesub layer comprises wood fibres and a binder and the average fibrelength in the sub layer is shorter than the average length of the woodfibres in the core.

The panel could have all surface layers mentioned above.

Overlay, decorative papers, core papers and HDF are made of individualfibres with a thickness of a few hundreds of a millimetre and a lengthof several millimetres, generally in the range of 3-5 mm. Thiscorresponds to a length/thickness ratio (LTR) of about 100. The sublayer according to the invention is formed of wood fibres that aremechanically cut into wood powder fibres. The average length of thefibres should preferably not exceed about 1 mm and this fibre length isconsiderably shorter than the length of the fibres in core. The LTR isin the region of about 30 or smaller. It is even more preferred that thefibres are smaller than 0.5 mm. Very high quality sub layers have beenobtained with very small fibres with an average length of 0.1-0.3 mm andan average LRT of less than 10.

Short fibres are easier to apply on a core in well-defined layers andthey provide a soft sub layer, which is easy to form and compress. Theyare easier to mix with resins especially is such resins are in drypowder form. Another advantage is that recycled and short fibres, whichare not possible to use in paper production due to low strength, couldbe used to form a strong sub layer.

According to a preferred embodiment of the second aspect of theinvention a building panel is provided, wherein the surface layercomprises upper portions and embossed portions lower than the upperportions wherein a part of the sub layer is more compressed under anembossed portion than under an upper portion.

It could be mentioned as a non-restricting example that the sub layercould comprise for example about 70-85% (weight) wood fibres and about15-30% melamine resin. The layer could have a thickness, which is forexample in the range of 0.1 mm-1 mm or even more. Other combinations areof course also possible. The mixture should be adapted to the desiredproperties and cost structures. The binders contribute in general togive the surface a high impact and moisture resistance but they arerather costly. Other hard and heavy particles such as aluminum oxide orstone powder could be included in the sub layer in order to increase thedensity and to improve the impact resistance.

It could be mentioned as a non-restricting example that the solidlaminate surface layer could comprise for example about 25% (weight)aluminum oxide, about 25% wood fibres, about 25% melamine resin andabout 25% colour pigments. The surface layer could have a thickness,which is for example in the range of 0.1 mm-3 mm or even more. Othercombinations are of course also possible. The melamine part could varyfor example between 10-35%. The content of the colour pigments could bevery low for example only about 0.1-5%. Wear resistant particles couldbe in the same range and could for example vary from a few percent to35% and even higher. The mixture should be adapted to the desiredproperties and cost structures.

The pressure is preferably about 300N-800N/cm² and the temperature couldbe 120-220 degrees C. The pressing time could vary for example from 20seconds to 5 minutes. It is possible to use very short pressing times,for example about 10 seconds or shorter, especially in embodiments wherea rather thin surface and sub layers are applied on an HDF core beforepressing. Thermoplastic binders such as PVC, PE, PP, etc could also beused.

It is preferred in all embodiments to use a dry process to form the sublayer and the solid laminate surface layer. The different materials andmixtures of different materials such as fibres, wear resistantparticles, binders and colour pigments are distributed and scattered ina dry form. Scattering could be made with several stations comprisingembossed or engraved rollers and brushes that could apply one or severallayers of dry material.

A panel could of course be formed without a surface layer. Only a sublayer as described above could be applied on a core. The sub layer,which in this case has a surface of wood fibres and binders, could bemade with a flat or embossed structure. A final decorative surface couldbe applied for example as a print in the factory or as a paint orcoating or similar by the consumer. The panel could also be used withoutany additional decorative layer over the sub layer. New types of corematerials could also be produced with for example a core and a sub layerapplied on the core. The advantage is that core materials could be usedwhich for example is not suitable to use in wood and laminate flooring.They could for example be too soft or difficult to laminate or glue. Thesub layer could however create a strong and suitable base for theapplication of a surface layer. More cost effective core materials orcore materials with other properties than HDF could be used. Decorativesub layers make it possible to form decorative grooves or bevels.

All preferred embodiments with and without wear resistant particlescould be used to make panels, which could be applied vertically on awall as wall panels in interior or exterior applications. Such panelscould have a mechanical locking system on long edges that is possible tolock with angling and optional on short edges a locking system with forexample a flexible tongue that allows vertical folding as described infor example WO 2006/043893.

A third aspect of an embodiment of the invention is floor productionequipment which comprises a roller with needles or engraved protrudingportions and a brush for applying dry materials comprising small woodfibres and binders and preferably wear resistant particles and colourpigments on a board material. The amount of needles or engravedprotruding portions should be adapted to the dry materials and to thetype and size of fibres, which are applied on the board material, toobtain an even flow of fibres and a clean roller after it has passed thebrush. In a preferred embodiment the amount of needles or the engravedprotruding portions is more than about 20 per cm² and most preferably inthe range of about 40-120 per cm². This equipment could also be used inthe production of WFF floor board as described in PCT/EP2008/065489.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-1 d illustrate a known floor panel with an embossed surface.

FIGS. 2 a-e illustrate a floor panel according to the invention.

FIGS. 3 a-d illustrate a production method to apply particles on a core.

FIGS. 4 a-c illustrate a panel surface and production method to form anembossed surface

FIGS. 5 a-c illustrate panels according to the invention.

FIGS. 6 a-d illustrate a panel surface with decorative grooves andbevels.

FIGS. 7 a-e illustrate a method to form an in register embossed surface.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 a shows a laminated floor panel 1 according to known technologycomprising a surface layer 5, a core 6 and a balancing layer 7. FIG. 1 cshows the surface layer 5. It has an upper wear layer 13 of atransparent material with great wearing strength. Such a wear layercomprises generally a transparent paper impregnated with melamine resinand with aluminum oxide particles 12 added. A decorative layer 10comprising paper with a printed pattern 11 is impregnated with melamineresin and placed under this transparent wear layer 13. The wear layer 13and the decorative layer 10 are laminated to the core, generally a fibrebased core such as HDF, under pressure and heat to an about 0.2 mm thicksurface layer 5. FIG. 1 b shows the balancing layer 7 that generallyalso is a melamine-impregnated paper. This balancing layer keeps thefloor panel flat when humidity varies over time. The transparent wearlayer is generally 0.05-0.10 mm thick.

FIG. 1 d shows a laminate flooring with an embossed surface layeraccording to known technology. The surface layer 5 comprises upperportions 5 a and embossed portions 5 b, which are compressed and locatedlower than the upper portions. The embossing is made to a depth of about0.1 mm and only the overlay 13 and the decorative paper (10) arecompressed.

FIGS. 2 a -2 d shows a floor panel 1 according to one embodiment of theinvention where the surface layer 5 is a Solid Laminate Surface Layer. Apanel 1 is provided with a wood fibre based core 6, a non-transparentdecorative surface layer 5 and preferably a balancing layer 7 as shownin FIG. 2 a. FIG. 2 b shows the surface layer 5 that comprises woodfibres 14, small hard wear resistant particles 12, 12′ and a binder 19.Preferably the wood fibres are unrefined and comprise lignin. Such wearresistant particles (12, 12′) are preferably aluminum oxide particles.Other suitable materials are for example silica or silicon carbide.Diamond crystals or powder, could also be added into the surface layer.In general all materials with a hardness of Rockwell C hardness HRC of70 or more could be used and they do not have to be transparent. Amixture of two or more materials could be used.

An embodiment of the invention offers the advantage that the wearresistant surface layer 5 could be made much thicker than in known floorpanels. The thickness of the wear resistant and decorative surface layercould vary from for example about 0.1 mm to for example about 4 mm oreven more. Wear resistance with maintained decorative properties couldbe extremely high, for example in the region of 100,000 revolutions ormore in a surface layer that is about 1.0 mm thick.

A preferable binder is melamine or urea formaldehyde resin. Any otherbinder, preferably thermosetting resins, could be used

FIG. 2 c show that a balancing layer 7 comprising preferably wood fibres14′ and a binder could be provided on the lower side of the floor panel.The fibres, the binder and also the pressing temperature should beadapted in an appropriate way to balance the surface layer and to keepthe panel flat. The balancing layer 7 is preferably pressed with ahigher temperature for example 5-20° C. higher than the surface layer 5

It could be mentioned as a non-restricting example that the surfacelayer could comprise of for example 25% (weight) aluminum oxide, 25%wood fibres, 25% melamine resin and 25% colour pigments. The surfacelayer could have a thickness, which is for example in the range of 0.1mm-3 mm or even more. The most preferable thickness is 0.5-1.5 mm.

The surface layer comprises preferably wood powder with particle whichare in the range of about 0.1-0.3 mm or even smaller.

A particularly high quality surface layer 5 could be achieved if thewood fibres, which are mixed with the binding agent, colour pigments andwear resistant particles, are already pre coated and fully or partly precured with a binder, for example a melamine or urea formaldehyde resin,or pressed and then separated mechanically into wood fibre powder orwood fibre chips which are preferably smaller and more compact than theoriginal wood fibres. Such a fibre composition is especially well suitedto be mixed with wear resistant particles and could create a welldefined base for the printing operation with wear resistant particlesevenly spread over the whole surface layer. Such coated fibres could beobtained from recycled HDF.

FIG. 2 d show a panel where the surface layer 5 has been formed on acore 6 that has been produced in a prior separate operation, for examplea HDF panel. There is a distinct connection 34 between the core 6 andthe surface layer 5. The connection 34 could be very strong sincebinders 19 from the surface layer 5 penetrate into the upper part of thecore 6, especially if the core is HDF or a wood based panel such as forexample particleboard. Different binders or binder contents could beused in the upper and lower parts of the surface layer 5. A sub layer 6a is applied between the surface layer 5 and the core 6. This sub layer6 a could be produced in the same way as the Solid Laminate SurfaceLayer described above and the same material compositions could be usedexcept for the fact that in some embodiments wear resistant particlesand colour pigments are not included. Such materials could however beincluded in the sub layer 6 a in order to for example create decorativegrooves or to increase the impact resistance. The binders 19 in the sublayer 6 a could be specially adapted to penetrate and reinforce theupper parts of the core 6 in order to for example increase the moistureresistance of the upper parts of the core.

FIG. 2 e shows that pressing a matrix to the surface 5 could creategrooves 37, bevels, grout lines and similar. Such embossing could bemade much deeper than in traditional laminate floorings where the paperwill be damaged. Embossing with a depth of for example 1-2 mm or evenmore could easily be obtained. The production cost could be decreased ifthe thickness of the surface layer 5 is reduced and replaced with a sublayer 6 a that only comprises wood fibres and binders. Such sub layercould increase impact resistance, reduce sound and create a layer thatcould be compressed and cured during pressing such that deep surfacestructures could be obtained which are deeper than the thickness of theSolid Laminate Surface Layer.

FIG. 3 a show a scattering station 60 which could be used to distributedry materials in layers in order to form a Solid Laminate Surface Layeror a sub layer 6 a. Fibres, wear resistant particles, binders in powderform and colour pigments in powder form could for example be mixed andapplied into an container 55 that is in contact with an engraved roller53. This roller 53 brings during rotation the mixed material 55 intocontact with a brush roller 54 and the material 55 is applied on aconveyor belt 20 or on another layer or board material. Liquid resins orwater 61 could be applied on the core or sprayed over the fibres inorder to stabilize the fibre layer prior to pressing. This facilitatesthe pressing and the application of a surface layer over the sub layer.It is preferred to use water containing for example 1% weight content ofa wetting agent for example BYK-348 from BYK Chemie which is applied onan core. 10-100 g/m² could be used. 10-20 g/m² is preferred. Other typesof wetting agents can also be used, as e.g., soap and the like.

Small wood fibres which are 1.0 mm or shorter and which are mixed withother dry materials such as melamine powder, colour pigments and smallwear resistant particles as described above are very difficult todistribute in well defined layers. Conventional scattering equipmentcannot be used. This problem could be solved if the surface of theroller 53 comprises a large amount of thin needles or spikes, which arepreferably made of a strong and polished metal. The amount of needles orspikes should be adapted to the type and size of fibres, and to theother dry materials, which are applied on the board, to obtain an evenflow of fibres and a clean roller after it has passed the brush. Furtherparameters, which should be considered, are the diameter and the lengthof the needles and the spikes. This is shown in FIG. 3 b. The length ofthe needles is preferably about 1 mm and the thickness about 0.5 mm.Very good results have been reached with rollers which comprises about80 needles/cm², needle diameters of 0.5 mm and needle lengths of 0.8 mm,as shown in FIG. 3 c. 40-120 needles/cm² could also be used depending onthe size of the powder particles and the material composition. Theroller 53 has preferably a diameter of about 100-300 mm. It is preferredto use an oscillating brush 54 that moves along the length of the roller53. Scattering equipment with such rollers could be used to applymaterials in powder form and to create Solid Laminate Surface Layers andsub layers as describe in all preferred embodiments. As a non-limitingexample it could be mentioned that 400 gr/m2 of powder material could beapplied with a speed of 10 m/min. This corresponds to a pressed sublayer of about 0.2 mm. Lower speed and/or several scattering stationscould be used if thicker layers are required.

An embodiment of the invention provides equipment and a method toproduce a floorboard by applying dry materials comprising small woodfibres and binders and preferably wear resistant particles and colourpigments on a board material. The equipment comprises a roller withneedles or engraved protruding portions and a brush. In a preferredembodiment the amount of needles or the engraved protruding portions ismore than about 20 per cm² and most preferably in the range of about40-120 per cm².

FIG. 3 d shows that several scattering stations 60 a, 60 b could be usedto apply one or several layers 5, 6 a on a core 6.

FIGS. 4 a-c show how a thin surface layer 5, preferably a wood veneerlayer, a printed paper with an overlay or a foil with a thickness of forexample 0.3-1.0 mm, could be formed with deep structures that give anappearance similar to solid wood. FIG. 4 a shows how a floorboard couldbe produced. A thin surface layer 5 is applied on a sub layer 6 acomprising for example cork or wood fibres mixed with a binder,preferably a thermosetting binder. The sub layer 6 a is applied on forexample a wood fibre based core, preferably a HDF core. Other corematerials could be used such as particleboard, plywood, plasticmaterials etc. A balancing layer 7 could also be applied to the core 6.FIG. 4 b show how the core and the layers are pressed together. Thispressing forms the sub layer 6 a and the surface layer 5, which arecured and connected to each other under heat and pressure. Very deepembossing could be obtained and a rough surface similar to hand scrapedsolid wood could be created with a thin wood veneer. The sub layer couldbe used to improve the properties of the surface layer, for examplesound absorption and impact resistance.

This sub layer comprises or consists of small individual fibres and anuncured binder and is applied on the core as a powder. The small fibresare not bonded to each other as for example long fibres in paper layersand a HDF core, and could easily be compressed, formed and displaced inall direction during the initial part of a pressing operation until thebinder cures. The uncured sub layer 6 a behaves similar to a paste or aliquid substance and creates a uniform counter pressure in all partsunder the surface layer even in surface parts with deep and sharpembossing.

The conversion from a layer of uncured unbonded fibres to a solid layercould be described by the following process:

-   -   1. A first step takes place when a heated press plate, or a        steel belt in case a continuous press is used, is in initial        contact with the surface layer and the protruding portions of        the press plate/belt are deforming parts of the surface layer.        The sub layer material, which is in powder form, is partly        displaced horizontally but also vertically upwards towards the        cavities of the press plate/belt where parts of the surface        layer could be pressed upwards into the cavities. A locally        increased compression of the core under the protruding portions        of the press plate/belt could take place if the sub layer is        thin or if the initial pressure is high or if the embossing is        deep. Such a compression of the core could however be avoided if        thicker sub layers are used.    -   2. The sub layer material will be converted to a paste form in a        second step when heat increases and the melamine binder becomes        liquid. The pressure is substantially evenly distributed in the        whole surface layer and sub layer. The pressure could now be        increased and this will not cause any increased local        compressions of the core or the surface layer.    -   3. A curing of the binders will take place in the final third        step when heat and pressure reaches the maxim level and the sub        layer will obtain its final properties related to shape and        density.

Materials, material compositions, heat and pressure could according toan embodiment of the invention be adapted in order to form a highquality surface even in the case when deep and sharp embossing incombination with thin surface layers are used as a surface in a buildingpanel. According to one preferred embodiment a panel with a HDF core andsurface layer is provided comprising a decorative paper, an overlay andan embossed structure with a depth that exceeds the thickness of thesurface layer and wherein the upper part of the HDF core is flat andessentially parallel with the horizontal plane HP.

The result is an improved and easier forming with lower pressing forceand improved surface quality. A thin surface layer will usually not bedamaged, significantly or at all, during pressing and the sub layer willafter curing provide a strong base for the thin surface layer. Such abase could be stronger than the core and improved impact resistancecould be reached.

Very deep embossing could be obtained with a surface layer thatcomprises conventional decorative paper and overlay used in conventionallaminate floorings. The pressure time and the pressing force could alsobe similar to conventional laminate production. Conventionally alamination pressure of about 400 N/cm² is used. Embossing depth wherethe compressed portions 5 b are about 0.3-1.0 mm below the upperportions 5 a can be made even when the surface structure comprisesrather sharp embossed portions, for example with an angle exceeding 45degrees against the horizontal plane HP, as shown in FIG. 4 c. Evendeeper structures could be made but such structures are generally notsuitable for floorings since they are difficult to clean and to placefurniture on. Such deep embossing could however be used in wall panelsand to form bevels at the edges of a floor panel.

FIGS. 5 a and 5 b show fibre structure of floor panels according topreferred embodiments of the invention. FIG. 5 a shows a floor panelwith a HDF core 6. Such a core comprises individual fibres with athickness of about 0.03 mm and a length of about 2-5 mm. The surfacelayer 5 comprises a decorative paper 10 and an overlay 13, whichcomprises individual fibres of the same size as the core 6. The sublayer 6 a comprises fibres, which are mechanically cut and essentiallyshorter. They have preferably an average length that does not exceed 1mm. This means that the fibres in the sub layer have an average lengthwhich is 50% or less than the average length of the wood fibres in thecore. Shorter fibres are even more preferred, for example of an averagesize of 30% of the length of core fibres or less. Very compact and highquality layers have been obtained with fibres, which have a length ofonly 0.1-0.3 mm. Such micro fibres are very suitable to form highquality Solid Laminate Surface Layers. Short fibres are easier to applyon a core in well-defined layers and they provide a soft sub layer,which is easy to form and compress to a solid and compact layer. Theyare easier to mix with resins especially if such resins are in drypowder form and a high internal bonding and moisture resistance could bereached. Another advantage is that recycled and short fibres, which arenot possible to use in paper production due to low bonding strength,could be used to form a strong sub layer in a floor panel. Long fibressimilar to fibres used in HDF and paper could be used to form a sublayer. Such a layer will however give a much lower quality and theproduction will be more complicated and costly.

FIG. 5 b shows a panel with a particleboard core 6. Such a core consistsof small wood chips 14 a comprising several fibres 14 which areconnected with glue to a board. The chips could have a thickness of0.5-1.0 mm and a length of 2-4 mm. Particleboard is softer and has alower density than HDF. The surface layer 5 is a Solid Laminate SurfaceLayer comprising short fibres. The sub layer comprises the same fibresize as the surface layer. The short fibres 14 in the two upper layers 6a, 5 could provide a very hard surface with high impact resistance evenin the case when the core 6 is made of a rather soft material. Highimpact resistance and a smooth surface layer similar to an HDF basedpanel can also be reached with a core of particleboard and with surfacelayers comprising paper or foil provided that the sub layer is compactand has a sufficient thickness to over bridge the irregularities of thesoft core surface under the sub layer.

FIG. 5 c shows that a panel could be made which only has a core 6 and asub layer 6 a. A balancing layer 7 could also be provided if needed.Such a panel could be used as composite core material in laminate andwood flooring production. Several sub layers 6 a with differentproperties regarding density, moisture, sound, flexibility etc. could beused. The sub layer should preferably have different materials ordifferent material properties than the core. Different combinations offibres, fibre size, density and binders could be used to make a costeffective core with high quality.

FIG. 6 a shows a panel with surface layers 5, and a sub layer 6 a withpreferably different design or structure. Decorative grooves 8 could beformed to a depth such that the lower sub layer 6 a is visible, as shownin FIG. 6 b. Very accurate and attractive design effects could beobtained. FIG. 6 c shows that embossing could be made in connection withpressing and that such embossing 5 b could form bevels at the edges of afloor panel when the floorboard and a floor panel is formed withmechanical locking systems. FIG. 6 d shows that sharp embossing with anangle A of 45 degrees and more, extending upwardly from the horizontalplane HP, could be made. 45-60 degrees is possible and even 90 degreescould be reached. Such deep embossing could be combined with for examplea surface layer 5 comprising paper sheets and with a depth D thatexceeds the thickness of the surface layer 5 and a core surface, whichis flat and parallel with the horizontal plane HP. No local compressionof the core 6 is needed and this simplifies the production and allowsdeeper embossing. Such embossing could be made with a depth D that is 2times or even three times deeper than the thickness of the surface layer5.

FIGS. 7 a-e show a preferable method to create a surface layer with anin register embossed surface (EIR), especially in a flooring accordingto embodiments of this disclosure. An embossed pressure matrix 23 isprovided preferably as a sheet, a structured paper, a roller, a belt andsimilar with a surface that comprises embossed protrusions 29 as shownin FIG. 7 a. A decorative material for example paint or coloured fibresor similar is applied on the protrusions 29 with an application devicefor example a rubber roller 28 or similar. A surface layer 5 comprisinguncured fibres and binders is provided as shown in FIG. 7 c and thepressure matrix 23 is pressed against the surface layer 5, as shown inFIG. 7 d. The decorative material 29 will be positioned at the lowestsurface portions and a perfect in register embossing will be obtained asshown in FIG. 7 e.

This method is very suitable for all types of surfaces where decorativeparts could be included in the surface during the final forming andcuring of the surface in a pressing operation. Paint could be used thatduring pressing penetrates into the basic fibre structure. A print couldbe applied into a fibre layer, on an overlay or decorative paper or on awood veneer.

A Solid Laminate Surface layer could be formed in several alternativeways. It is possible to produce such surface layer without colourpigments or wear resistant particles. A thermosetting binder, forexample melamine, could in some embodiments be sufficient, if it is forexample combined with fibres, preferably wear resistant fibres, thatcould be used to replace the wear resistant particles. Plastic fibres orgranulates, for example nylon fibres or mineral fibres such as glassfibres, could improve the wear resistance considerably in a basicsurface layer material that also comprises wood fibres.

It is also possible to replace wood fibres in the Solid Laminate SurfaceLayer completely or partly with other fibres such as vegetable fibresfor example jute, linen, flax, cotton, hemp, bamboo, bagasse and sisaland to use wear resistant particle, for example aluminium oxide, tocreate a vegetable fibre based wear resistant surface layer.

Wood fibres in the sub layer could also partly or completely be replacedwith plastic fibres or granulates, mineral fibres or vegetable fibres inthe same way as described above for the surface layer and the same typeof materials could be used.

The sub layer could also be used to produce for example a compositelaminate similar to a conventional high-pressure laminate. Suchconventional laminates consists of one, or several phenol impregnatedcore papers under a melamine impregnated decorative paper. The laminateis generally glued to a board. All or some of the core papers could bereplaced with a sub layer comprising small wood fibres and binders asdescribed in any of the preferred embodiments above. The mix of woodfibres and binders could for example be applied on a core paper. Thefibres in the mix are preferably smaller than the fibres in the corepaper or the decorative paper. A decorative paper could be applied onthe mix of wood fibres and binders. Wood fibres, binders, core paper anddecorative paper could be subjected to heat and pressure until thebinder cures. Such a composite laminate could also be produced without acore paper. A fibre layer could be applied directly on a release paper,a steal sheet or most preferably on a steal belt of a continuous press.

A composite laminate as described above is more cost efficient thanconventional laminates. Deeper embossing, increased impact resistanceand flexibility and a better sound level could for example be reached ifone or several core papers are replaced with a wood fibre layer.Decorative grooves and bevels could be formed if the sub layer comprisescolour pigments. Such a sub layer of a composite laminate could have athickness of for example 0.1-1.0 mm and the total thickness of the solidlaminate could be about 0.2-1.2 mm. Ticker layers of for example 1-3 mmor more are also possible.

The composite laminate could for example be glued to a board and usedfor example as a floor panel, wall panel or a furniture component.

All surface layers as described in the preferred embodiments could beused to form a composite layer in the same way as described above forthe composite laminate. A wood veneer, preferably with a thickness of0.3-1.0 mm, could for example be used in combination with a sub layer toproduce a 2-4 mm veneer composite layer, which could be applied on alamella core and used in an 12-15 mm engineered parquet floor in orderto replace a 3 mm parquet strip of solid wood. Foils and Solid LaminateSurface Layers could be combined with wood fibres and binders in orderto form a composite layer. All of the above described embodiments couldbe used individually or in combinations.

Using an overlay with wear resistant particles is not excluded and thiscould increase the wear resistance of a wood veneer. Dry and wetoverlays, which are produced by production methods where for examplethermosetting resins in dry or wet form are mixed with aluminum oxidewithout any fibres, could also be used. Aluminum oxide particles mixedwith melamine powder could for example be applied on a wood veneer priorto pressing and a wear resistant surface could be obtained without anysurface coating after pressing.

1. A method of manufacturing a floor board (1) comprising a wood fibrebased core (6), a thin surface layer (5) and a sub layer (6 a) betweenthe surface layer and the core, the sub layer comprises wood fibres (14)and a binder (19), wherein the method comprises the steps of: mixingparticles comprising wood fibres (14) and an uncured binder (19) for thesub layer (6 a); applying the wood fibres (14) and the uncured binder(19) for the sub layer on the core (6); applying a surface layer (5) onthe wood fibres (14) and the uncured binder (19); and bringing the core(6), the surface layer (5), the wood fibres (14) and the uncured binder(19) under increased pressure and temperature and forming them into afloor board (1) by curing the binder (19).
 2. The method as claimed inclaim 1, wherein the method further comprises the step of pressing thesurface layer 5) with an embossed pressing matrix (23) such that thesurface layer (5) obtains upper portions (5 a) and embossed portions (5b) lower than the upper portions essentially by shaping of the sublayer.3. The method as claimed in claim 1, wherein the core (6) is HDF.
 4. Themethod as claimed in claim 1, wherein the thin surface layer (5) has athickness of about 0.3-1.0 mm.
 5. The method as claimed in claim 1,wherein the binder (19) in the sub layer (6) is a thermosetting resin.6. The method as claimed in claim 1, wherein the method furthercomprises applying water or a liquid resin on the core (6) or into thefibres (14) of the sub layer (6 a) prior to pressing.
 7. The method asclaimed in claim 1, wherein the surface layer (5) comprises a homogenousmix of wood fibre particles (14), wear resistant particles (12), binders(19) and colour pigments (15).
 8. The method as claimed in claim 7,wherein the wear resistant particles (12) comprise aluminum oxide. 9.The method as claimed in claim 1, wherein the surface layer (5)comprises a binder (19) of a thermosetting resin.
 10. The method asclaimed in claim 1, wherein the surface layer (5) comprises a binder(19) of a thermoplastic resin.
 11. The method as claimed in claim 1,wherein the surface layer (5) is a printed paper (10) with an overlay(13).
 12. The method as claimed in claim 1, wherein the surface layer(5) is a wood veneer.
 13. The method as claimed in claim 1, wherein themethod comprises a machining operation comprising forming the floorboard to a floor panel (1) with mechanical locking systems (4, 4′) atopposite edges.
 14. The method as claimed in claim 1, wherein the stepof applying the wood fibres and the binder is with a roller (53)comprising needles (62) or engraved protruding portions (63).
 15. Themethod as claimed in claim 14, wherein the amount of needles (62) or theengraved protruding portions (63) is about 40-120 per cm².
 16. Abuilding panel comprising a thin surface layer (5), a wood fibre basedcore (6) and a sub layer (6 a) between the surface layer (5) and thecore (6), the sub layer (6 a) comprises wood fibres (14) and a binder(19) wherein the sub layer (6 a) comprises fibres with an average length(L2) which is shorter than the average length (L1) of the wood fibres inthe core (6).
 17. The building panel as claimed in claim 16, wherein thesurface layer (5) comprises upper portions (5 a) and embossed portions(5 b) lower than the upper portions (5 a) whereby a part of the sublayer (6 a) is more compressed under an embossed portion (5 b) thanunder an upper portion (5 a).
 18. The building panel as claimed in claim16, wherein the average length (L2) of the fibres in the sub layer (6 a)does not exceed 50% of the average length (L1) of the fibres in the core(6).
 19. The building panel as claimed in claim 18, wherein the length(L2) of the fibres in the sub layer (6 a) does not exceed 30% of thelength (L1) of the fibres in the core (6).
 20. The building panel asclaimed in claim 16, wherein the building panel is a floor panelcomprising a balancing layer (7).
 21. The building panel as claimed inclaim 16, wherein the binder (19) in the sub layer (6 a) is athermosetting resin.
 22. The building panel as claimed in claim 21wherein the binder (19) in the sub layer (6 a) is a melamine resin. 23.The building panel as claimed in claim 16, wherein the binder (19) inthe sub layer (6 a) comprises a thermosetting resin.
 24. The buildingpanel as claimed in claim 16, wherein the core (6) comprises HDF. 25.The building panel as claimed in claim 16, wherein the thin surfacelayer (5) comprises a substantially homogenous mix of wood fibres (14),which comprise natural resins, a binder (19) and wear resistantparticles (12).
 26. The building panel as claimed in claim 25, whereinthe wear resistant particles (12) comprise aluminum oxide.
 27. Thebuilding panel as claimed in claim 26, wherein the surface layer (5)further comprises colour pigments (15) and a melamine resin.
 28. Thebuilding panel as claimed in claim 16, wherein the surface layer (5) isa wood veneer.
 29. The building panel as claimed in claim 16, whereinthe surface layer (5) comprises a decorative paper (10) and an overlay(13).
 30. The building panel as claimed in claim 17, wherein the surfacelayer (5) comprises a decorative paper (10) and an overlay (13) and theembossed portions (5 b) comprise a part with an edge which is formedwith an angle (A) exceeding 45 degrees to the horizontal plane (HP). 31.The building panel as claimed in claim 30, wherein the embossed portions(5 b) comprise a part with a depth (D) that exceeds the thickness of thesurface layer (5) and wherein the upper part of the core (6) is flat andessentially parallel with a horizontal plane (HP).
 32. The buildingpanel as claimed in claim 16, wherein the surface layer (5) comprises afoil comprising a thermoplastic resin.
 33. The building panel as claimedin claim 16, wherein the surface layer has a thickness which does notexceed 1.0 mm.
 34. The building panel as claimed in claim 16, whereinthe sub layer comprises cork particles.
 35. Floorboard productionequipment (60) comprising a roller (53) with needles (62) or engravedprotruding portions (63) and a brush (54) for applying dry materialscomprising small wood fibres (14) and binders (19) on a board material(6).
 36. The equipment as claimed in claim 35, wherein the amount ofneedles (62) or the engraved protruding portions (63) is more than about20 pieces per cm².
 37. The equipment as claimed in claim 35, wherein theamount of needles (62) or the engraved protruding portions (63) is about40-120 pieces per cm₂.
 38. The equipment as claimed in claim 35, whereinthe dry materials comprise wear resistant particles (12) and colourpigments (15).
 39. A building panel comprising a thin surface layer, awood fiber core, and a sub layer between the surface layer and the core,the sub layer comprising wood fibers and a binder, wherein the sub layeris formed by applying loose wood fiber particles and an uncured binderon the wood fiber core, and the sub layer and the surface layer areconnected to each other under heat and pressure so as to cure the binderin the sub layer.
 40. A building panel comprising a thin surface layer,a wood fiber core, and a sub layer between the surface layer and thecore, the sub layer comprising wood fibers and a binder, wherein thesurface layer and sub layer are connected to each other under heat andpressure by curing scattered wood fiber particles of the sub layer. 41.A building panel comprising a thin surface layer, a wood fiber core, anda sub layer between the surface layer and the core, the sub layercomprising wood fibers and a binder, wherein the wood fibers of the sublayer are oriented randomly.
 42. A building panel comprising a thinsurface layer, a wood fiber core, and a sub layer between the surfacelayer and the core, the sub layer comprising wood fibers and a binder,wherein panel is formed by a method comprises the steps of: mixingparticles comprising loose wood fiber particles and an uncured binderfor the sub layer; applying the loose wood fiber particles and theuncured binder for the sub layer on the core; applying a surface layeron the loose wood fiber particles and the uncured binder; and bringingthe core, the surface layer, the loose wood fiber particles and theuncured binder under increased pressure and temperature and forming theminto a floor board by curing the binder.